Integrated circuits, the key components in thousands of electronic and computer products, are interconnected networks of electrical components fabricated on a common foundation, or substrate. Fabricators generally build these circuits layer by layer, using techniques, such as deposition, doping, masking, and etching, to form and interconnect thousands and even millions of microscopic transistors, resistors, and other electrical components on a silicon substrate, known as a wafer.
One common technique for forming layers in an integrated circuit is called chemical vapor deposition. Chemical vapor deposition generally entails placing a substrate in a reaction chamber, heating the substrate to prescribed temperatures, and introducing one or more gases, known as precursor gases, into the chamber to begin a deposition cycle. The precursor gases enter the chamber through a gas-distribution fixture, such as a gas ring or a showerhead, one or more centimeters above the substrate, and descend toward the heated substrate. The gases react with each other and/or the heated substrate, blanketing its surface with a layer of material. An exhaust system then pumps gaseous by-products or leftovers from the reaction out of the chamber through a separate outlet to complete the deposition cycle.
Conventional chemical-vapor-deposition (CVD) systems suffer from at least two problems. First, conventional CVD systems generally form non-uniformly thick layers that include microscopic hills and valleys, and thus generally require use of post-deposition planarization or other compensation techniques. Second, it is difficult, if not impossible, for CVD to provide uniform coverage of trench sidewalls or complete filling of holes and trenches.
To address these shortcomings, fabricators have developed atomic-layer deposition (ALD), a special form of CVD that allows highly uniform formation of ultra-thin layers having thicknesses of one molecule or several atoms of the deposited material. Though similar to CVD in terms of equipment and process flow, ALD relies on adsorption of some of the reactants into exposed surfaces, and thus provides coverage and fill of structural features that are difficult, if not impossible, using CVD.
In recent years, researchers and engineers have made strides toward making ALD commercially viable for some applications. For example, one team of researchers reportedly optimized an ALD process for depositing an aluminum oxide (AlOx) film in thin-film heads—devices used to read and write magnetic data. See, Paranjpe et al., Atomic Layer Deposition of AlOx for Thin Film Head Gap Applications, Journal of Electrochemical Society, 148 (9), pp. G465-G471 (2001), which is incorporated herein by reference.
However, the present inventors have recognized that the equipment and processes reported as optimal for thin-film head applications suffer from some limitations relative to use in fabricating integrated circuits. For example, the reported process deposits material at the slow rate of less than one Angstrom per cycle, suggesting that more than 50 cycles would be necessary to form a 50-Angstrom-thick layer. Moreover, the reported equipment uses a larger than desirable reaction chamber, which takes longer to fill up or pump out, and thus prolongs the duration of each deposition cycle.
Accordingly, there is a need for better systems and methods of atomic-layer deposition of aluminum oxides as well as other material compositions.